Photochemotherapic method of treating psoriasis by using methylangelicin compounds

ABSTRACT

The alkylangelicins according to the invention are obtained starting from an umbelliferone, in which the 6-position is already substituted by an alkyl group; in such a way the 7-allyloxy or 7-acyloxy umbelliferone intermediates can form by transposition of the allyl or acyl group only the 8-allyl and 8-acyl derivatives, and therefore the presence, even in traces, of psoralens is absolutely excluded in the subsequent synthetic steps. 
     The 6-alkylangelicins thus obtained are particularly usable for the photochemotherapy of psoriasys and of other skin diseases characterized by cellular hyperproliferation, as well as for the photochemotherapy of vitiligo and of alopecia aerata.

This is a continuation of application Ser. No. 922,342, filed Oct. 23, 1986, now abandoned, which is a continuation of Ser. No. 541,064, filed Oct. 12, 1983 now abandoned.

The present invention concerns a process of producing alkylangelicins (angular furocoumarins) free from psoralens (linear furocoumarin) and alkylangelicins obtained therefrom, particularly to be used for the photochemotherapy of psoriasis and of other skin diseases characterized by cellular hyperproliferation, as well as for the photochemotherapy of vitiligo and of alopecia aerata.

It is well known that the photochemotherapy of psoriasis, of mycosis fungoides and of other skin diseases characterized by cellular hyperproliferation is carried out with the combined action of psoralens (bifunctional linear furocoumarins) and long wave ultraviolet light; this therapy is also known as PUVA from psoralens+UV-A light (320-400 nm) (Parrish et al. New Eng. J. Med.--291, 1207 (1974)).

This treatment utilizes the property of the psoralens to photodamage the skin cellular DNA in a selective way.

The antiproliferative activity is due to the mono-and bifunctional photodamages to DNA (in this latter case to inter-strand cross-links formed between two bases appertaining to the two complementary strands of the macromolecule) induced by the psoralens at cellular level.

Another property exploited by the psoralens consists in their capability of inducing the skin pigmentation; also in this case the effect is obtained through the combined action of psoralens and long wave-length ultraviolet light (UV-A). This property is used in therapy for the treatment of vitiligo or leucodermia (A.M. El Mofty "Vitiligo and psoralens" Pergamon Press, Oxford, 1968).

The PUVA therapy may be carried out either by oral administration, or by topical application of psoralens and subsequent irradiation with UV-A light.

This therapy is considered as the most effective in the case of some kinds of psoriasis, in the initial phase of mycosis fungoides and for vitiligo; however, several side effects have been evidenced, as the risk of cutaneous cancer (R. S. Stern et al "Risk of Cutaneous Carcinoma in Patients treated with oral Methoxalen Photochemotherapy for Psoriasis", N. Eng. J. Med. 300,852 (1979)), the risk of hepatoxicity (H. Tronnier et al, "Photochemotherapy in Dermatology, in "Photochemotherapy: Basic Technique and Side Effects", Proceedings of the German-Swedish Symposium on Photomedicine in Oberursel--West Germany--p. 71 Apr. 23-25 1975, ed. E. G. Jung, Schattauer Verlag, Struttgart--New York, 1976) and of cataract (S. Lerman et al, "A Method for Detecting 8-methoxypsoralen in the Ocular Lens" Science 197,1287 (1977)) in the case of oral administration of psoralens. Furthermore the problem of the skin phototoxicity exists and it results enlarged in particular for topical application of psoralens. In fact it is well known that psoralens, also in very low doses (1-5 μg/cm²) photoinduce a painful and troublesome erythema on the skin of the human or the guinea-pig; after some days, a dark pigmentation follows this erythema (M.A. Pathak et al. Bioassay of Natural and Syntetic Furocoumarin (psoralens), J. Inv. Dermatol, 32,509 (1959)).

Some studies concerning this object seem to indicate that the skin phototoxicity is essentially due to bifunctional lesions photoinduced in the skin cell DNA by the psoralens (F. Dall'Acqua and F. Bordin "Recent aspects of photobiological properties of furocoumarins, in the molecular basis of dermatological diseases" M. A. Pathak and P Chandra Eds. Plenum, NY in press ); furthermore other studies seem to indicate that also the genotoxic effect (in terms of mutagenic activity), to which the cancerogenic activity of psoralens is clearly related, is mostly due to the cross-links (L. Dubertret et al. "Psoralens in cosmetic and dermatology" J. Cahn et al. Eds. Pergamon Press, 1981, p. 245).

In order to eliminate these undesired effects of psoralens, some monofunctional furocoumarins have been proposed, i.e. furocoumarins able to induce only monofunctional photodamages to cellular DNA. In particular it has been proposed to use the angelicin modified by introduction of one or more alkyl groups, with the aim to increase both the capacity of photoreacting with the DNA and the antiproliferative activity. In particular the alkyl groups have been introduced in 4-, 5-, 4'- and 5'-position.

The alkylangelicins thus obtained have shown a strong affinity towards DNA also in the dark; they form a molecular complex with the macromolecule and for subsequent irradiation induce very efficiently and selectively monofunctional photodamages to DNA, showing a strong antiproliferative activity.

These known alkylangelicins, and in particular the methylangelicins have shown a strong activity in the therapy of psoriasis, by topical application, showing at the same time, at the therapeutic doses, to be practically unable to cause skin phototoxicity; furthermore, their genotoxicity have proved to be generally lower than that of psoralens (U.S. Pat. No. 4,312,883).

However, the preparation of these compounds by chemical synthesis has shown some difficulties for reaching purity levels acceptable not only for laboratory search experiments on their antiproliferative activity, but most of all for their clinical experimentation. Actually the synthesis of these alkylangelicins starts from suitable O-prenyl-umbelliferones or O-acyl-umbelliferones, in which the alkyl or acyl group is rearranged (Claisen or Fries) in the 8-position. Such a transposition is not univocal, as other than in the 8-position, it occurs in the 6-position too. The 6-prenyl or 6-acyl intermediates originate, during the subsequent synthetic steps, alkylpsoralens (i.e. linear furocoumarins), which are isomers of alkylangelicins.

Considering that methylpsoralens are very effective in inducing inter-strand cross-linkages in DNA, their presence, even if in traces in the angelicins can deeply modify the photobiological and phototherapeutic properties of the same angelicins. In particular the methylpsoralens show an extremely high skin-phototoxic activity (Rodighiero et al. I1 Farmaco "Photochemical and photobiological properties of 4,5'-dimethylpsoralens" Ed-Sci 36,648,1981; G. Caporale et al. "Skin Photosensitizing activity of some methylpsoralens" Experientia 23 985 (167)).

For this reason the synthesis of the above mentioned alkylangelicins involves a time-consuming an expensive step necessarily careful, concerning the separation of the essential 8-allyl intermediates or 8-acylumbelliferones from the corresponding 6-isomers.

According to the invention the problem is solved with a process of producing alkylangelicins free from psoralens, of formula ##STR1## wherein R is alkyl, R₁, R₂, R₃, R₅ are independently hydrogen or alkyl, R₆ is hydrogen, alkyl, hydroxymethyl, acetoxymethyl, methoxymethyl as well as aminomethyl, alkylaminomethyl, dialkylaminomethyl, or a group of formula ##STR2## wherein R₇ and R₈ are simultaneously hydrogen, methyl or ethyl, free or salified, characterized in that a 6-alkylumbelliferone O-derivative, with formula ##STR3## wherein R, R₁, R₂, R₃ have the meaning above referred to and, R₄ is an acyl residue of formula

    --CO--R.sub.9

wherein R₉ is an alkyl group or an allyl residue of formula

    --CHR.sub.10 --CH═CHR.sub.11

wherein R₁₀ and R₁₁ are independently hydrogen or alkyl, is submitted to Fries or Claisen rearrangement, thus yielding respectively the compounds ##STR4## then, in the case of compound (3), it is condensed with ethylbromoacetate, subsequently hydrolized to acid and then cyclized by acetic anhydride and sodium acetate, thus yielding a 6-alkylangelicin of formula (1) wherein R₅ is hydrogen and R₆ is an alkyl group, while in the case of compound (4), it is acetilated, brominated, cyclized in alkaline medium, thus giving a 6-alkylangelicin of formula (1), wherein R₅ is alkyl and R₆ is hydrogen or alkyl, or, after being previously ozonized and reduced with hydrogen and catalyst to α,α-alkyl(8-coumarinyl)acetaldehyde, it is cyclized in acidic medium, thus giving a 6-alkylangelicins of formula (1), wherein R₅ is hydrogen, and, when R₆ of the compound (1) is hydrogen, it is converted, through a treatment with chloromethylmethylether, into the corresponding 4'-chloromethylangelicin, which is then converted into the corresponding 4'-hydroxymethyl, 4'-acetoxymethyl, 4'-aminomethyl, 4'-alkylaminomethyl, 4'-dialkylaminomethyl or 4'-aminoethoxymethyl or 4'-dimethylaminoethoxymethyl or 4'-diethylaminoethoxymethyl derivatives, and finally, to obtain water-soluble compounds, the derivatives containing the amino group, substituted or not, are converted into the corresponding hydrochloride.

The alkylangelicins obtained through the process according to the invention are characterized by a general formula ##STR5## wherein R is alkyl, R₁, R₂, R₃ and R₅ are independently hydrogen or alkyl, R₆ is hydrogen, alkyl, hydroxymethyl, acetoxymethyl, methoxymethyl, as well as aminomethyl, alkylaminomethyl, dialkylaminomethyl or a group of formula ##STR6## wherein R₇ and R₈, are simultaneously hydrogen, methyl or ethyl, free or salified.

Advantageously the alkylangelicins according to the invention can be selected from the group comprising 6-methylangelicin, 6,5-dimethylangelicin, 6,5'-dimethylangelicin, 6,5,5'-trimethylangelicin, 6,4,5'-trimethylangelicin, 6,4-dimethylangelicin, 6,4'-dimethylangelicin, 6,5,4'-trimethylangelicin and 6,4,4'-trimethylangelicin.

Substantially the 6-alkylangelicins according to the present invention are obtained starting from an umbelliferone, in which the 6-position is already substituted by an alkyl group; in such a way the 7-allyloxy or 7-acyloxy umbelliferone intermediates, can form by transposition of the allyl or acyl group only the 8-allyl and 8-acyl derivatives, and therefore the presence, even in traces, of psoralens is absolutely excluded in the subsequent synthetic steps.

SYNTHESIS OF THE 6ALKYLANGELICINS

The present invention is hereinafter further clarified with reference to the following examples. Unless differently indicated, the amounts and the percentages are related to the weight.

EXAMPLE 1

A mixture of 2,4-dihydroxytoluene (18.7 g), malic acid (18.7 g) and conc. H₂ SO₄ (37 ml) was gently heated up till the gaseous development almost ceased. The deep-red reaction mixture was then poured under vigorous stirring into boiling water (300 ml) and the suspension was kept under stirring until the gummy mass initially formed was completely dispersed. The solid was collected by filtration, dried and crystallized from absolute EtOH, yielding 6-methyl-7-hydroxycoumarin (I) (14.5 g; m.p. 253°-4° C. with dec.). ##STR7##

EXAMPLE 2

In a manner similar to example 1, from 3,5-dihydroxy-2-methyltoluene (9.6 g) the 5,6-dimethyl-7-hydroxycoumarin (II), crystallized from MeOH (8.5 g; m.p. 262° C. with dec.) was obtained. ##STR8##

EXAMPLE 3

A solution of 2,4-dihydroxytoluene (10.0 g) in ethylacetoacetate (12 ml) was poured in small portion into conc. H₂ SO₄ (26 ml), chilling in an ice bath. After the addition was completed the solid obtained was separated by filtration, washed several times with water up to neutrality of the washings, dried and crystallized from MeOH, yielding 4,6-dimethyl-7-hydroxycoumarin (III) (10.64 g; m.p. 273° C.). ##STR9##

EXAMPLE 4

A mixture of 6-methyl-7-hydroxycoumarin (I) (14.5 g), anhydrous K₂ CO₃ (5 g), allyl bromide (15 ml) and acetone (400 ml) was refluxed for 12 h under stirring. From the refluxed mixture the solid was filtered and washed several times with acetone. The acetonic solution and the pooled washings were concentrated to dryness and the residue crystallized from MeOH, yielding 6-methyl-7-allyloxycoumarin (IV) (11.4 g; m.p. 124°-5° C.). ##STR10##

EXAMPLES 5-6

In a manner similar to example 4, from 5,6-dimethyl-7-hydroxycoumarin (II) (5.0 g) 5,6-dimethyl-7-allyloxycoumarin (V) was obtained, crystallized from MeOH (3.8 g; m.p. 123° C.). ##STR11##

From 4,6-dimethyl-7-hydroxycoumarin (III) (9.6 g) 4,6-dimethyl-7-allyloxycoumarin (VI) was obtained, crystallized from MeOH (10.0 g; m.p. 134° C.). ##STR12##

EXAMPLE 7

A solution of 6-methyl-7-hydroxycoumarin (IV) (11.4 g) in diethylaniline (80 ml) was refluxed for 2 h. After cooling the solution was diluted with n-hexane (500 ml) yielding a precipitate, which was collected by filtration, washed several times with n-hexane and crystallized from EtOAc, yielding 6-methyl-7-hydroxy-8-allylcoumarin (VII) (6.3 g; m.p. 161°-2° C.). ##STR13##

EXAMPLES 8-9

In a manner similar to example 7, from 5,6-dimethyl-7-allyloxycoumarin (V) (2.0 g) 5,6-dimethyl-7-hydroxy-8-allylcoumarin (VIII) was obtained, crystallized from EtOAc/Cyclohexane (1.2 g; m.p. 169°-70° C.). ##STR14##

From 4,6-dimethyl-7-allyloxycoumarin (VI) (9.5 g) 4,6-dimethyl-7-hydroxy-8-allycoumarin (IX) was obtained, crystallized from EtOAc/Cyclohexane (6.2 g; m.p. 179°-80° C). ##STR15##

EXAMPLE 10

To prepare those alkylangelicins with an alkyl group on the furan ring, the 8-allylcoumarins were acetylated and brominated, yielding the 8-(2',3'-dibromopropyl) derivatives, which were then cyclized with ethanolic KOH, to give the corresponding 5'-methylangelicins.

In such a manner a mixture of 6-methyl-7-hydroxy-8-allylcoumarin (VII) (6.3 g), anhydrous AcONa (1.5 g) and acetic anhydride (40 ml) was refluxed for 1 h. The reaction mixture was gently diluted with water (40 ml), refluxed for 10 min and then poured into H₂ O (300 ml) yielding a precipitate, which was collected by filtration and washed several times with H₂ O. The dried product was crystallized from MeOH yielding 6-methyl-7-acetoxy-8-allylcoumarin (X) (6.1 g; m.p. 110°-11° C.). ##STR16##

EXAMPLES 11-12

In a manner similar to example 10, from 5,6-dimethyl-7-hydroxy-8-allylcoumarin (VIII) (2.5 g) 5,6-dimethyl-7-a-cetoxy-8-allylcoumarin (XI) was obtained, crystallized from MeOH (2.2 g; m.p. 148°-9° C.); ##STR17##

From 4,6-dimethyl-7-hydroxy-8-allylcoumarin (IX) (3 g) 4,6-dimethyl-7-acetoxy-8-allylcoumarin (XII) was obtained, crystallized from MeOH (2.4 g; m.p. 139°-140° C.). ##STR18##

EXAMPLE 13

Into an acetic solution (100 ml) of 6-methyl-7-a-cetoxy-8-allylcoumarin (X) (7 g) an acetic solution (50 ml) containing the stoichiometric amount of bromine was added dropwise at room temperature.

After the addition was completed the solution was stirred for 30 min., the solvent was evaporated under reduced pressure and the solid residue crystallized from MeOH giving the 6-methyl-7-acetoxy-8-(2',3'-dibromopropyl) coumarin (XIII) (6.8 g; m.p. 154°-5° C.). ##STR19##

EXAMPLES 14-15

In a manner similar to example 13 from 5,6-dimethyl-7-acetoxy-8-allylcoumarin (XI) (2.6 g) 5,6-dimethyl-7-acetoxy-8-(2',3'-dibromopropyl)coumarin (XIV) was obtained, crystallized from MeOH (2.1 g; m.p. 168-9° C.). ##STR20##

From 4,6-dimethyl-7-acetoxy-8-allylcoumarin (XII) (2.3 g) 4,6-dimethyl-7-acetoxy-8-(2',3'-dibromopropyl)coumarin (XV) was obtained, crystallized from MeOH (1.5 g; m.p. 135-137° C.). ##STR21##

EXAMPLE 16

To an ethanolic solution (100 ml) of 6-methyl-7-acetoxy-8-(2',3'-dibromopropyl) coumarin (XIII) (1.5 g) a volume of ethanolic 4% KOH solution was added, equivalent to a molar ratio coumarin/KOH 1:10. The mixture was refluxed for 80 min. in the dark, chilled, diluted with H₂ O (200 ml) and acidified with dil. HC1. The precipitate thus obtained was filtered, washed with H₂ O, dried and chromatographed on a silica gel column by eluting with CHC1₃, yielding the 6,5'-dimethylangelicin (XVI), crystallized from MeOH (0.52 g; m.p. 175-6° C.). ##STR22##

EXAMPLES 17-18

In a manner similar to example 16 from 5,6-dimethyl-7-acetoxy-8-(2',3'-dibromopropyl) coumarin (XIV) (1.07 g) 6,5,5'-trimethylangelicin (XVII) was obtained, crystallized from MeOH (0,38 g; m.p. 204-5° C.). ##STR23##

From 4,6-dimethyl-7-acetoxy-8-(2',3'-dibromopropyl)coumarin (XV) (2.1 g) 6,4,5'-trimethylangelicin (XVIII) was obtained, crystallized from MeOH (0.62 g; m.p. 183° C.). ##STR24##

EXAMPLE 19

The following procedure is used to prepare the alkylangelicins without alkyl groups on the furan ring. The 8-allyl derivatives of the coumarins (VII), (VIII), (XI) were ozonized and then reduced, thus yielding the 8-coumarinylacetaldehydes, which were then cyclized with 85% H₃ PO₄.

The 6-methyl-7-hydroxy-8-allylcoumarin (VII) (1.7 g) was dissolved in EtOAc (150 ml) and into the solution, cooled in an ice bath, a stream of ozonized oxigen was bubbled until 1.1 times the stoichiometric amount of ozone was reached. The solution was then immediately submitted to hydrogenation in the presence of Pd 10% on CaCO₃ (0,3 g) and the mixture stirred until the rapid absorption of hydrogen ceased. The catalyst was removed by filtration, the solvent evaporated at reduced pressure, and the residue treated with 85% H₃ PO₄ (60 ml). The reaction mixture was then placed into a thermostatic bath at 100° C. for 20 min, chilled, diluted with H₂ O (200 ml) and extracted with CHCl₃. From the dried (Na₂ SO₄) organic phase the solvent was evaporated under reduced pressure and the residue chromatographed on a silica gel column by eluting with CHCl₃, yielding the 6-methylangelicin (XIX), crystallized from MeOH (0.18 g; m.p. 164°-5° C.). ##STR25##

EXAMPLES 20-21

In a manner similar to example 19 from 5,6-dimethyl-7-hydroxy-8-allylcoumarin (VIII) (2.0 g) the 6,5-dimethylangelicin (XX) was obtained, crystallized from MeOH (0.21 g; m.p. 219°-20° C.). ##STR26##

From 4,6-dimethyl-7-hydroxy-8-allylcoumarin (IX) (3.2 g) the 6,4-dimethylangelicin (XXI) was obtained, crystallized from MeOH (0.42 g; m.p. 150°-1° C.). ##STR27##

EXAMPLE 22

To prepare the alkylangelicins with an alkyl group in the 4'-position of the furan ring, the suitable umbelliferones, (I), (II), (III) were acetylated and the 7-acetoxycoumarins thus obtained were submitted to the Fries rearrangement. The 8-acetylumbelliferones were converted into the ethyl esters of the 7-(8-acetylcoumarinyl)oxyacetic acids, which were then hydrolized and cyclized yielding the desired 4'-methylangelicins. In such a manner a mixture of 6-methyl-7-hydroxycoumarin (I) (10.0 g), acetic anhydride (40 ml) and anhydrous AcONa (4.0 g) was refluxed for 1 h. To the reaction mixture an equal volume of H₂ O was cautiously added and the whole was refluxed for 10 min. The mixture was diluted with H₂ O (300 ml), chilled and the precipitate was collected by filtration, washed several times with H₂ O, dried and crystallized from MeOH, yielding the 6-methyl-7-acetoxycoumarin (XXII) (10.0 g; m.p. 147° C.). ##STR28##

EXAMPLES 23-24

In a manner similar to example 22 from 5,6-dimethyl-7-hydroxycoumarin (II) (5.0 g) 5,6-dimethyl-7-acetoxycoumarin (XXIII) was prepared, crystallized from MeOH (4,6 g; m.p. 206° C.). ##STR29##

From 4,6-dimethyl-7-hydroxycoumarin (III) (8.0 g) 4,6-dimethyl-7-acetoxycoumarin (XXIV) was prepared, crystallized from MeOH (7.8 g; m.p. 160°-1° C.). ##STR30##

EXAMPLE 25

A mixture of 6-methyl-7-acetoxycoumarin (XXII) (2.0 g), anhydrous AlCl₃ (4.4 g) and NaCl (2.0 g) was heated at 160°-170° C. for 1,5 h. The reaction mixture, after cooling was disgregated in dil. HCl (50 ml), refluxed for 10 min, then poured into H₂ O (200 ml) and extracted with EtOAc. The dried organic phase (Na₂ SO₄) gave by evaporation of the solvent a residue which was crystallized from MeOH yielding the 6-methyl-7-hydroxy-8-acetylcoumarin (XXV) (1.1 g; m.p. 170° C.). ##STR31##

EXAMPLE 26-27

In a manner similar to example 25, from 5,6-dimethyl-7-acetoxycoumarin (XXIII) (3.0 g) 5,6-dimethyl-7-hydroxy-8-acetylcoumarin (XXVI) was obtained, crystallized from EtOAc (0.95 g; m.p. 216°-8° C.). ##STR32##

From 4,6-dimethyl-7-acetoxycoumarin (XXIV) (3 g) 4,6-dimethyl-7-hydroxy-8-acetylcoumarin (XXVII) was obtained, crystallized from MeOH (1.05 g; m.p. 236°-7° C.). ##STR33##

EXAMPLE 28

A mixture of 6-methyl-7-hydroxy-8-acetylcoumarin (XXV) (1.8 g) and of ethyl bromoacetate (3 ml) dissolved into acetone (50 ml) and in the presence of anhydrous K₂ CO₃ was refluxed for 3 h. After cooling the solid was eliminated by filtration and the solvent evaporated under reduced pressure. The residue was crystallized from EtOAc/cyclohexane yielding the ethyl ester of the 7-(6-methyl-8-acetylcoumarinyl)oxyacetic acid (XXVIII) (1.7 g; m.p. 88°-9° C.). ##STR34##

EXAMPLES 29-30

In a manner similar to example 28 from 5,6 -dimethyl-7-hydroxy-8-acetylcoumarin (XXVI) (1.4 g) the ethyl ester of the 7-(5,6-dimethyl-8-acetylcoumarinyl)oxyacetic acid (XXIX) was obtained, crystallized from EtOAc/cyclohexane (0.8 g; m.p. 109° C.). ##STR35##

From 4,6-dimethyl-7-hydroxy-8-acetylcoumarin (XXVII) (3.2 g) the ethyl ester of the 7-(4,6-dimethyl-8-acetylcoumarinyl)oxyacetic acid (XXX) was obtained, crystallized from EtOAc/cyclohexane (2.2 g; m.p. 96°-7° C.). ##STR36##

EXAMPLE 31

The ethyl ester of the 7-(6-methyl-8-acetylcoumarinyl)oxyacetic acid (XXVIII) (1.8 g) was dissolved into a water-methanolic solution (1/1) of 5% KOH (70 ml) and the solution was refluxed for 15 min, in the dark. After cooling and acidification with dil. HCl, the solution was diluted with H₂ O (200 ml) and the solid precipitate was collected by filtration, dried and crystallized from EtOAc/cyclohexane, yielding the 7-(6-methyl-8-acetylcoumarinyl)oxyacetic acid (XXXI; 1.1 g; m.p. 196°-7° C.). ##STR37##

EXAMPLES 32-33

In a manner similar to example 31, from the ethyl ester of the 7-(5,6-dimethyl-8-acetylcoumarinyl)oxyacetic acid (XXIX) (1.7 g) the 7-(5,6-dimethyl-8-acetylcumarinyl)oxyacetic acid (XXXII) was obtained, crystallized from MeOH (1.3 g; m.p. 219°-20° C.). ##STR38##

From the ethyl ester of the 7-(4,6-dimethyl-8-acetylcoumarinyl)oxyacetic acid (XXX; 1.9 g) the 7-(4,6-dimethyl-8 -acetylcoumarinyl)oxyacetic acid (XXXIII) was obtained, crystallized from EtOAc (1.35 g; m.p. 184°-6° C.). ##STR39##

EXAMPLE 34

A mixture of 7-(6-methyl-8-acetylcoumarinyl)oxyacetic acid (XXXI; 3.7 g), anhydrous AcONa (3 g) and acetic anhydride (30 ml) was refluxed for 1 h. In such conditions the compound (XXXI) underwent cyclization also accompanied by a nearly complete decarboxylation. To the mixture H₂ O (30 ml) was gently added and the whole was again refluxed for 10 min. The cooled reaction mixture was diluted with H₂ O (300 ml), made alkaline by NaHCO₃ addition and the suspension was extracted several times with EtOAc. From the dried organic phase (Na₂ SO₄) the solvent was evaporated and the residue crystallized from MeOH, yielding the 6,4'-dimethylangelicin (XXXIV; 2.1 g; m.p. 156°-7° C.). ##STR40##

EXAMPLES 35-36

In a manner similar to example 34 from the 7-(5,6-dimethyl-8-acetylcoumarinyl)oxyacetic acid (XXXII) (2.2 g) the 6,5,4'-trimethylangelicin (XXXV) was obtained, crystallized from MeOH (1.15 g; m.p. 229° C.). ##STR41##

From the 7-(4,6-dimethyl-8-acetylcoumarinyl)oxyacetic acid (XXXIII; 1.7 g) the 6,4,4'-trimethylangelicin (XXXVI) was obtained, crystallized from MeOH (0.85 g; m.p. 201°-2° C.). ##STR42##

DISCUSSION OF THE PHARMACOLOGICAL PROPERTIES OF THE 6-ALKYLANGELICINS

The 6-alkylangelicins according to the invention show an appreciable technical progress with respect to the known alkylangelicins, and this either under the aspect of the therapeutic security, being they absolutely free from psoralens, or under the aspect of the preparation facility.

In fact the total lacking of psoralens make sure that the high antiproliferative activity is only due to monofunctional lesions to DNA, and at the same time allows to obtain a compound through a process more quick, more simple, less expensive and having a higher efficiency.

PHOTOBINDING CAPACITY OF THE 6-ALKYLANGELICINS TO DNA

The 6-alkylangelicins show a strong affinity with DNA in the dark, thus forming molecular intercalated complexes; moreover the 6-methylangelicins complexed to DNA by irradiation bind very strongly to the macromolecule, inducing only monofunctional lesions (Table I).

ANTIPROLIFERATIVE ACTIVITY OF THE 6-ALKYLANGELICINS IN PRECLINICAL TESTS

The 6-alkylangelicins show a strong antiproliferative activity in Ehrlich ascites tumor cells (Table II) and on the skin of mice in terms of DNA synthesis inhibition (Table III). These compounds are practically unable to induce skin phototoxicity on albino guinea-pig skin (Table II).

                                      TABLE I     __________________________________________________________________________     Binding parameters of the complexes between 6-alkylangelicins and DNA     and rate constant of their photoreactions with the macromolecule.                                    rate constant ×     Compound    K values                          -n.sup.a                            1/ -n.sup.b                                    min.sup.-1 × 10.sup.2     __________________________________________________________________________     angelicin    560    15.87                            0.063 ± 0.003                                    1.10     6-methylangelicin                  925 ± 64                         20.83                            0.048 ± 0.002                                    3.60     6,4-dimethylangelicin                 2,990 ± 232                         15.87                            0.063 ± 0.003                                    5.23     6,4'-dimethylangelicin                 6,300 ± 541                         16.39                            0.061 ± 0.003                                    9.90     6,5'-dimethylangelicin                 1,975 ± 136                         12.82                            0.078 ± 0.004                                    3.00     6,4,4'-trimethylangelicin                 10,100 ± 1190                         10.99                             0.091 ± 0.0045                                    13.30     6,4,5'-trimethylangelicin                 3,310 ± 281                         22.22                            0.045 ± 0.002                                    7.02     6,5,5'-trimethylangelicin                 3,730 ± 339                         14.29                             0.070 ± 0.0035                                    2.30     8-MOP.sup.c  736.sup.c                         7.81.sup.c                            0.128.sup.c                                    3.10     __________________________________________________________________________      .sup.a According to McGhee and Von Hippel, (J. Mol. Biol., 86, 469, 1974)      -n is defined here as the number of nucleotides occluded by one bound      molecule of angelicin derivative.      .sup.b 1/-n defines, according to McGhee and Von Hippel, the frequency of      binding sites; in other words, the number of ligands bound per nucleotide      and can be considered analogous to the "-n" value obtained by the classic      Scatchard method (Ann. N.Y. Acad. Sci., 51, 660, 1949).      .sup.c As reference compound; data taken from Dall'Acqua et al. J. Invest      Dermatol., 29, 283, 1979.

                  TABLE II     ______________________________________     Photobiological properties of 6-alkylangelicins              Inhibition of DNA              synthesis in Ehrlich              ascites tumor cells.sup.a                              skin                ID.sub.50 (quanta ×                            Relative  erythemogenic     Furocoumarin                10.sup.-18) ± S.E.                            activity  activity.sup.a     ______________________________________     8-MOP.sup.b                13.8 ± 0.6                            181       ++     angelicin  25.0 ± 1.1                            100       -     6-methylangelicin                26.3 ± 1.4                            95        -     6,4-dimethyl-                 4.0 ± 1.3                            625       -     angelicin     6,4'-dimethyl-                 2.28 ± 0.68                            1096      -     angelicin     6,5'-dimethyl-                11.87 ± 0.77                            210       -     angelicin     6,4,5'-trimethyl-                3.87 ± 1.5                            646       -     angelicin     6,4,4'-trimethyl-                 0.06 ± 0.007                            41666     -     angelicin     ______________________________________      .sup.a Determined according to Bordin et al., Il Farmaco, Ed. Sc., 36,      506, 1981.      .sup.b As reference sample.

                  TABLE III     ______________________________________     Inhibition of epidermal DNA synthesis in the mouse "in vivo"     after topical application (50 μg/cm.sup.2) of the compound and     UV-A irradiation (9 J/cm.sup.2).sup.a.     Furocoumarin     % inhibition ± S.E.     ______________________________________     No drug solvent alone                       2.5 ± 1.3     8-MOP.sup.b       61.0 ± 1.6     angelicin.sup.b   17.5 ± 2.5     6-methylangelicin                       29.25 ± 13.3     6,4-dimethylangelicin                      47.05 ± 4.3     6,4'-dimethylangelicin                      36.56 ± 3.9     6,5-dimethylangelicin                      52.83 ± 2.3     6,5,5'-trimethylangelicin                       36.01 ± 11.7     ______________________________________      .sup.a Determined according to Bordin et al., Il Farmaco, Ed. Sc., 36,      506, 1981.      .sup.b Reference compounds.

CAPACITY TO INDUCE DARK PIGMENTATION ON HUMAN SKIN

The 6-alkylangelicins are able to induce a dark pigmentation on human skin, without however inducing erythema at the therapeutical doses (Table IV).

                                      TABLE IV     __________________________________________________________________________     Results of topical photochemotherapy with 6-alkylangelicins in psoriatic     patients.               6-METHYL                       MAXIMA         %       ERYTHEMA PIGMENTAL               ANGELICINS                       DOSE OF                             N° OF                                      CLEARANCE                                              INDUCTION                                                       CAPACITY     N°       NAME SEX               (6-MA)  UV-A  TREATMENTS                                      6-MA                                          8-MOP                                              6-MA                                                  8-MOP                                                       6-MA                                                           8-MOP     __________________________________________________________________________     1 P.G. M. 6,4'-DMA                       8 J/cm.sup.2                             15       100%                                          85% -   -    +   ++     2 M.S. F. 6,4'-DMA                       9 J/cm.sup.2                             15        90%                                          70% -   +    +   ++     3 B.M. F. 6,4,4'-TMA                       8 J/cm.sup.2                             11       100%                                          75% -   +    +++ +     4 U.A. F. 6,4,4'-TMA                       4 J/cm.sup.2                             11        95%    -   .sup. +++.sup.a                                                       +   -     5 D.B.V.            F. 6,4,4'-TMA                       10 J/cm.sup.2                             15        90%                                          90% -   +++  ++  +     6 F.B. F. 6,4,4'-TMA                       6 J/cm.sup.2                              9       100%                                          80% -   .sup. +++.sup.b                                                       +   +     7 C.M.P.            F. 6,4,4'-TMA                       6 J/cm.sup.2                              9       100%                                          85% -   ++   +   ++     __________________________________________________________________________      .sup.a The treatment with 8MOP was stopped after 4 applications for sever      bollous reaction.      .sup.b The treatment with 8MOP was stopped after 5 application because of      severe erythema.      +++Very strong      ++Strong      +Moderate      -Absent      DMA Dimethylangelicin      TMA Trimethylangelicin

TOXICITY OF THE 6-ALKYLANGELICINS

The 6-alkylangelicins show a small toxicity, lower than that of 8-MOP (8-metoxypsoralen), the drug of first choice for the PUVA therapy. For example the 6,4'-dimethylangelicin, administered in methylcellulose suspension, show an acute toxicity having the following values, expressed in terms of LD₅₀ in mice:

per i.p. (intraperitoneum) 0.75 g/Kg (0.3 g/Kg for 8-MOP)

per os >2 g/Kg (0.75 g/Kg for 8-MOP).

THERAPEUTICAL ACTIVITY OF THE 6-ALKYLANGELICINS

The genotoxicity, in terms of mutagenic activity, of 6-alkylangelicins is much lower than that of 8-MOP (Table V).

                  TABLE V     ______________________________________     Mutagenic activity of 6-alkylangelicins on E. coli WP2-uvr A by     irradiation with UV-A.sup.a.                  n° of mutants per 10.sup.6 survivors                  irradiation time (seconds)     Furocoumarin   10      20     30    60   90     ______________________________________     8-MOP.sup.b    0.4     1.15   1.5   3.1  7.0     6,4-dimethylangelicin                    0.24    0.7    0.99  1.83 --     6,4'-dimethylangelicin                    0.96    1.76   2.63  --   --     6,4,4'-trimethylangelicin                    0.84    1.18   1.24  1.98 --     6,4,5'-trimethylangelicin                    0.62    0.91   1.23  1.93 --     ______________________________________      .sup.a The test was performed at the furocoumarin concentration of 5      μg/ml according to Venturini et al., Chem. Biol. Interactions, 30, 203      1980.      .sup.b As reference compound.

The therapeutical effectiveness of two 6-alkylangelicins, that is 6,4'-dimethylangelicin and 6,4,4'-trimethylangelicin, which have been chosen among the various new compounds on the basis of their antiproliferative activity, of their low genotoxicity and of their absence of skin phototoxicity on guinea-pig skin, were tested by measuring their capacity to clear psoriatic lesions in various patients (see Table IV).

For a comparative evaluation, the efficacy of 8-MOP (8-methoxypsoralen), the most used agent for PUVA, has also been tested in the same experimental conditions.

In the treated patients various areas 4×4 cm of the affected skin were used:

(a) in the first area an ethanolic solution (0.1% W/V) of the compound under investigation, was applied until a concentration of 5 μg/cm² was reached and left to evaporate by the heat of the body (or by hot air stream).

After 20 minutes the area was irradiated with a high intensity UV-A emitting low pressure mercury fluorescent lamp type PUVA WALDMANN SYLVANIA F 15 T 8.

The irradiation doses were selected in the range between 2.5-13 J/cm² ; in particular the initial dose was 2.5 J/cm² and this was gradually increased till 13 J/cm² was reached on the basis of the skin tolerance.

(b) In a second area an ethanolic solution of 8-methoxypsoralen (8+MOP) was applied to a concentration of 5 μg/cm² and the area was irradiated in a strictly similar way as in (a).

(c) a third area was treated in the same way as area (a), but was not irradiated with UV-A;

(d) a fourth area was irradiated as in (a) with the same dose of UV-A light in the absence of any compound.

The treatment with the two 6-methylangelicins was repeated generally 5 times a week for 2 or 3 weeks. A good clearing of the psoriatic lesions was generally observed after 9 treatments, while in the case of 8-MOP for the same treatments the extent of clearing was clearly lower (about 80%). In addition 6-methylangelicins appeared to be entirely uncapable of inducing skin-erythema even in the patients in which 8-MOP induced severe phototoxic response.

The area treated with the angelicin derivatives but not with UV-A did not show any improvement, while the area treated with UV-A alone showed a very low improvement.

While 6,4'-dimethylangelicin induced an evident dark pigmentation in the treated area, less pronounced than that induced by 8-MOP in the same conditions, 6,4,4'-trimethylangelicin appears more active.

The antiproliferative activities have been documented by hystological examinations of bioptical specimens carried out on the tested areas, soon after the treatment and one month later.

The strong activity of the 6-alkylangelicins according to the invention in inhibiting the epidermal DNA synthesis of mice after oral administration (see Table VI) allows to consider these compounds effective also by oral administration in humans and UV-A irradiation.

The following pharmacological compositions may be used for oral administration of the 6-alkylangelicins:

    ______________________________________     Capsules:     ______________________________________     6-alkylangelicin (drug)                            30 mg     Lactose (diluent)      70 to 120 mg     Mg stearate (lubricant)                            1 to 1.5 mg     Na Lauril sulphate (wetting)                            1.5 mg     ______________________________________

contained in a convenient hard or soft gelatine capsule.

    ______________________________________     Tablets     ______________________________________     6-alkylangelicin (drug)   30     mg     Lactose (diluent)         240    mg     Mg stearate (lubricant)   2      mg     Maize starch (disintegrant and lubricant)                               60     mg     Microcrystalline cellulose (lubricant                               10     mg     and disintegrant)     Polyvynilpyrrolidone (binder)                               3%     Na Lauril sulphate (wetting)                               3      mg     ______________________________________

one or more capsules or tablets, according to the body weight, age and sex of the patient, to be orally administered two hours before irradiation.

                  TABLE VI     ______________________________________     Inhibition of epidermal DNA synthesis in the mouse "in vivo"     after oral administration of the compound     (250 mg/kg) and UV-A irradiation (9 J/cm.sup.2).sup.a.     FUROCOUMARIN     % inhibition ± S.E.     ______________________________________     angelicin.sup.b  28.0 ± 2     8-MOP.sup.b      39.1 ± 3.7     6-methylangelicin                      19.65 ± 9.2     6,4-dimethylangelicin                      58.4 ± 13.0     6,4,5'-trimethylangelicin                      36.8 ± 8.5     6,4,4'-trimethylangelicin                      67.72 ± 8.2     6,5,5'-trimethylangelicin                      60.6 ± 14.1     6,5-dimethylangelicin                      50.12 ± 19     6,4'-dimethylangelicin                      49.23 ± 8.0     6,5'-dimethylangelicin                      22.48 ± 12.0     ______________________________________      .sup.a Determined according to Bordin et al., Il Farmaco, Ed. Sc., 36,      506, 1981.      .sup.b Reference compounds. 

We claim:
 1. A method of treating psoriasis and other skin diseases characterized by cellular hyperproliferation, of vitiligo and of alopecia aerata, as well as for inducing dark pigmentation on the human skin, comprising administering a therapeutically effective amount of methylangelicin compound,a member selected from the group consisting of 6,4-dimethylangelicin, 6,4'-dimethylangelicin, 6,4,5'-trimethylangelicin and 6,4,4'-trimethylangelicin. 